The present invention relates to a magnetic recording medium and a base film for the same. More specifically, it relates to a magnetic recording medium which has excellent electromagnetic conversion characteristics and a small reduction in output when it is repeatedly used and a base film for the same.
Remarkable progress has recently been made to increase the density of a magnetic recording medium, and the development and implementation of a ferromagnetic metal thin film magnetic recording medium comprising a ferromagnetic metal thin film formed on a non-magnetic base film by a physical deposition method such as vacuum deposition or sputtering, or plating are now underway. For example, there are known a Co-deposited tape (JP-A 54-147010) (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and a Coxe2x80x94Cr alloy vertical magnetic recording medium (JP-A 52-134706).
As conventional coated magnetic recording media (magnetic recording media comprising a magnetic layer formed on a non-magnetic base film by mixing magnetic powders with an organic polymer binder and applying the resulting mixture) have a low recording density and a long recording wavelength, the magnetic layer has a large thickness of about 2 xcexcm or more. In contrast to this, a metal thin film formed by thin film forming means such as vacuum deposition, sputtering or ion plating has a very small thickness of 0.2 xcexcm or less.
Therefore, in the above high-density magnetic recording medium, the surface state of a non-magnetic base film has a great influence upon the surface properties of a magnetic recording layer. That is, the surface state of the non-magnetic base film appears as the unevenness of the surface of the magnetic recording layer directly which causes noise in recording and reproduction signals. Therefore, the surface of the non-magnetic base film is desirably as smooth as possible.
On the other hand, from the viewpoints of handling properties such as conveyance, scratching, winding-off and winding-up in the formation of a non-magnetic base film and the film formation process, if the surface of the film is too smooth, slipperiness between films degrades, resulting in a reduction in product yield and an increase in production cost. Therefore, the surface of the non-magnetic base film is preferably as rough as possible from the viewpoint of production cost.
Thus, the surface of the non-magnetic base film is required to be smooth from the viewpoint of electromagnetic conversion characteristics whereas it is required to be rough from the viewpoints of handling properties and production cost.
Further, in the case of a metal thin film magnetic recording medium, a treatment called xe2x80x9cion bombardmentxe2x80x9d that the surface of a base film is activated by ions is made before a metal thin film is formed in order to improve adhesion between the metal thin film and the base film.
Since high-temperature heat is applied to the front side of the film when this metal thin film is formed, the rear side of the film is cooled to prevent the fusion of the base film or deterioration in the physical properties such as mechanical properties of the film. To cool the rear side of the film, the base film is often wound round a drum-like cooling material. At this point, both ends of the base film are masked to prevent the formation of a metal thin film on the surface of the drum.
Accordingly, a portion whose surface is activated by ion bombardment and devoid of a metal thin film is continuously existent at both ends of a sample roll subjected to the above deposition step in a longitudinal direction. When the film is rolled, this portion is contacted to the opposite side of the film at a high pressure, there by readily causing blocking. To produce a metal thin film magnetic recording medium, after a metal thin film is deposited, aback coat layer and optionally a top coat layer are formed. If the above blocking occurs in the step of processing these layers, the base film will be readily broken or wrinkled with the result of a great reduction in yield.
To solve the above problem, JP-A 9-207290 and JP-A 9-226063 propose a laminated film consisting of a layer A and a layer B whose surface is rougher than the surface of the layer A. However,this method cannot suppress a reduction in output at the time of repeated use and the occurrence of the above blocking though electromagnetic conversion characteristics, handling properties and winding properties can be balanced to a certain extent.
It is an object of the present invention to provide a polyester base film for magnetic recording media, which overcomes the above defect of the prior art and has excellent electromagnetic conversion characteristics, a small reduction in output at the time of repeated use and high running durability.
It is another object of the present invention to provide a laminated thermoplastic resin base film for magnetic recording media, which overcomes the above defect of the prior art, has excellent anti-block properties, winding properties and processability and gives a metal deposition thin film magnetic recording medium having excellent electromagnetic conversion characteristics.
It is still another object of the present invention to provide a magnetic recording medium which comprises a magnetic layer on the above base film of the present invention and has excellent characteristic properties such as electromagnetic conversion characteristics.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a polyester base film for magnetic recording medium (may be referred to as xe2x80x9cfirst base film of the present inventionxe2x80x9d hereinafter), which comprises a polyester film containing first inert fine particles having an average particle diameter of primary particles of 30 to 120 nm and a volume shape coefficient of 0.1 to xcfx80/6 and having a density of protrusions derived from the first inert fine particles on the surface of the film of 5,000 to 50,000/mm2 and an agglomeration rate of the first inert fine particles forming the protrusions on the surface of the film of 4 to 20%.
According to the present invention, secondly, the above objects and advantages of the present invention are attained by a laminated thermoplastic resin base film for magnetic recording medium (may be referred to as xe2x80x9csecond base film of the present inventionxe2x80x9d hereinafter), consisting of a first thermoplastic resin layer having a surface roughness WRa of the exposed surface of 0.1 to 4 nm and a second thermoplastic resin layer which contains 0.001 to 5 wt % of third inert fine particles having an average particle diameter of primary particles of 0.1 to 2.0 xcexcm and 0.001 to 10 wt % of an ester wax of an aliphatic monocarboxylic acid having 8 or more carbon atoms and a polyhydric alcohol and which has a water contact angle with the exposed surface of 70 to 90xc2x0, the first thermoplastic resin layer and the second thermoplastic resin layer being laminated together.
Thirdly, the above objects and advantages of the present invention are attained by a magnetic recording medium comprising either one of the first base film and the second base film of the present invention as a base film and a magnetic layer formed on the base film
A description is first given of the first base film of the present invention.
The polyester used in the present invention is an aliphatic, alicyclic or aromatic polyester. Out of these, an aromatic polyester is particularly preferred.
Examples of the aromatic polyester include polyethylene terephthalate, polyethylene isophthalate, polytetramethylene terephthalate, poly-1,4-cyclohexylenedimethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate. Out of these, polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate are preferred.
The polyester may be a homopolyester or copolyester. In the case of a copolyester, examples of a comonomer for polyethylene terephthalate or polyethylene-2,6-naphthalene dicarboxylate include other diol components such as diethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, polyethylene glycol, 1,4-cyclohexanedimethanol and p-xylylene glycol, other dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid (in the case of polyethylene-2,6-naphthalene dicarboxylate), 2,6-naphthalenedicarboxylic acid (in the case of polyethylene terephthalate) and 5-sodium sulfoisophthalic acid, and oxycarboxylic acid components such as p-oxyethoxybenzoic acid. The amount of the comonomer is 20 mol % or less, preferably 10 mol % or less based on the total of all the diol components in the case of a diol component or the total of all the dicarboxylic acids and oxycarboxylic acids in the case of dicarboxylic acid component and an oxycarboxylic acid component.
A polyfunctional compound having a functionality of 3 or more, such as trimellitic acid or pyromellitic acid, may be further copolymerized. In this case, it may be copolymerized in an amount that the polymer is substantially linear, for example, 2 mol % or less based on the total of all the dicarboxylic acid components.
The polyester film of the present invention (may be referred to as xe2x80x9cpolyester layer Axe2x80x9d hereinafter) contains first inert fine particles (may be referred to as xe2x80x9cinert particles Axe2x80x9d hereinafter). Examples of the inert particles A include heat resistant organic polymer fine particles such as crosslinked silicone resin, crosslinked polystyrene, crosslinked styrene-divinylbenzene copolymer, polymethyl methacrylate, methyl methacrylate copolymer, crosslinked methyl methacrylate copolymer, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile and benzoguanamine resin; and inorganic compounds such as silica, alumina, titanium dioxide, kaolin, talc, graphite, calcium carbonate, feldspar, molybdenum disulfide, carbon black and barium sulfate.
The average particle diameter of primary particles of the inert particles A is 30 to 120 nm, preferably 35 to 110 nm, more preferably 40 to 100 nm. When the average particle diameter is smaller than 30 nm, satisfactory running durability cannot be obtained and when the average particle diameter is larger than 120 nm, electromagnet conversion characteristics deteriorate.
As for the shape of the inert particles A, the volume shape coefficient (f) represented by the following equation (I) is 0.1 to xcfx80/6, preferably 0.3 to xcfx80/6, more preferably 0.4 to xcfx80/6:
f=V/R3xe2x80x83xe2x80x83(I)
wherein f is a volume shape coefficient, V is the volume (xcexcm3) of each particle, and R is the average particle diameter (xcexcm) of the particles.
The inert particles A having a volume shape coefficient (f) of xcfx80/6 are globular (spherical). That is, the inert particles A having a volume shape coefficient (f) of 0.4 to xcfx80/6 are substantially globular, spherical or oval like a rugby ball which are particularly preferred. The particles having a volume shape coefficient (f) of less than 0.1, for example, flaky particles deteriorate running durability disadvantageously.
The density of protrusions derived from the inert particles A on the surface of the polyester layer A is 5,000 to 50,000/mm2, preferably 7,500 to 45,000/mm2, more preferably 10,000 to 40,000/mm2. When the density of protrusions derived from the inert particles A on the surface is lower than 5,000/mm2, the friction of the magnetic layer with the magnetic head becomes high and the running durability of the magnetic layer at the time of repeated use deteriorates disadvantageously. When the density of protrusions is higher than 50,000/mm2, more protrusions fall off with the result of more drop-outs disadvantageously.
The density of protrusions can be adjusted by the concentration and/or amount of a glycol slurry of particles which is added when the polyester is polymerized.
The agglomeration rate of the inert particles A on the surface of the polyester layer A is 4 to 20%, preferably 5 to 18%, more preferably 6 to 16%, particularly preferably 7 to 14%. When the agglomeration rate of the particles is lower than 4%, running durability at the time of repeated use becomes unsatisfactory and a marked reduction in output is seen. When the agglomeration rate is higher than 20%, electromagnetic conversion characteristics deteriorate.
The agglomeration rate of the particles can be adjusted by controlling the pH of the above glycol slurry of the particles which is added when the polyester is polymerized and reaction thereof, or by controlling the reaction process, temperature and injection speed for injecting the above slurry.
Another layer such as a coating layer or another polyester layer may be formed on one side or both sides of the first base film of the present invention in limits not prejudicial to the object of the present invention so as to improve the characteristic properties of a magnetic tape such as handling properties at the time of production and processing.
For instance, when a magnetic tape is produced from the first base film of the present invention, a first coating layer (may be referred to as xe2x80x9ccoating layer Bxe2x80x9d hereinafter) which contains second inert fine particles (may be referred to as xe2x80x9cinert particles Bxe2x80x9d hereinafter) having an average particle diameter of 10 to 50 nm and a volume shape coefficient of 0.1 to xcfx80/6 is formed on the magnetic layer side of the polyester layer A containing inert particles A in order to prevent a reduction in output (deterioration durability in still mode) caused by repeated contact with the magnetic head. Preferably, the above coating layer B has a density of protrusions derived from the inert particles B on the surface of 2,000,000 to 20,000,000/mm2 and a surface roughness (Ra) of 0.1 to 2.0 nm.
The inert particles B contained in the above coating layer B are preferably inert particles which hardly settle in a coating solution and have relatively low specific gravity. Preferred examples of the inert particles B include heat resistant polymer particles made of materials such as crosslinked silicone resin, crosslinked acrylic resin, crosslinked polystyrene, melamine.formaldehyde resin, aromatic polyamide resin, polyamide-imide resin, crosslinked polyesters and wholly aromatic polyesters, silicon dioxide (silica) and calcium carbonate. Particularly preferred are crosslinked silicone resin particles, core-shell type organic particles (core: crosslinked polystyrene, shell: polymethyl methacrylate) and silica.
The average particle diameter of primary particles of the inert particles B is 10 to 50 nm, preferably 15 to 45 nm, more preferably 20 to 40 nm. When the average particle diameter is smaller than 10 nm, the slipperiness of the obtained film may become unsatisfactory and when the average particle diameter is larger than 50 nm, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
The inert particles B have a volume shape coefficient (f) of 0.1 to xcfx80/6, preferably 0.2 to xcfx80/6, more preferably 0.3 to xcfx80/6, particularly preferably 0.4 to xcfx80/6. Particles having a volume shape coefficient (f) of less than 0.1, for example, flaky particles make it difficult to obtain the effect of improving the slipperiness of the film.
The density of protrusions derived from the inert particles B on the surface of the coating layer B is 2,000,000 to 20,000,000/mm2, preferably 3,000,000 to 15,000,000/mm2, more preferably 3,500,000 to 12,000,000/mm2. When the density of protrusions on the surface of the coating layer B is lower than 2,000,000/mm2, the slipperiness of the obtained film may become unsatisfactory and when the density of protrusions is higher than 20,000,000/mm2, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
The surface roughness (Ra) of the coating layer B is 0.1 to 2.0 nm, preferably 0.2 to 1.8 nm, more preferably 0.3 to 1.6 nm. When the surface roughness (Ra) is lower than 0.1 nm, the slipperiness of the obtained film may become unsatisfactory and when the surface roughness is higher than 2.0 nm, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
The surface roughness (Ra) can be adjusted by the particle diameter and/or amount of the inert particles B to be contained in the coating layer B.
In the coating layer B, a binder resin is used to bind the inert particles B. The binder resin is preferably an aqueous polyester resin, aqueous acrylic resin or aqueous polyurethane resin, particularly preferably an aqueous polyester resin.
Examples of the aqueous polyester resin include polyester resins each of which consists of at least one polycarboxylic acid such as isophthalic acid, phthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4xe2x80x2-diphenyldicarboxylic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, succinic acid, sodium 5-sulfoisophthalate, potassium 2-sulfoterephthalate, trimellitic acid, trimesic acid, monopotassium salt of trimellitic acid or p-hydroxybenzoic acid as an acid component and at least one polyhydroxy compound such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, p-xylylene glycol, dimethylol propane or bisphenol A adduct with ethylene oxide as a glycol component; graft polymers and block copolymers prepared by binding an acrylic polymer chain to a polyester chain; and acryl modified polyester resins comprising two different polymers which form a specific physical structure in the micro-particle (IPN (inter-penetrating polymer network) type or core-shell type). The aqueous polyester resin may be any type which is soluble, emulsifiable or finely dispersible in water. A sulfonate group, carboxylate group or polyether unit may be introduced into the molecule of the polyester resin to provide hydrophilic nature.
It is possible and preferred to form a coating layer and/or another polyester layer on the side opposite to the magnetic layer side when a magnetic tape is to be produced from the polyester film of the present invention in order to improve handling properties at the time of producing and processing the film.
For instance, when a second coating layer (may be referred to as xe2x80x9ccoating layer Cxe2x80x9d hereinafter) which contains fourth inert fine particles (may be referred to as xe2x80x9cinert particles Cxe2x80x9d hereinafter) having an average particle diameter of primary particles of 20 to 80 nm is formed on the side opposite to the magnetic layer side, when a magnetic tape is to be produced of the polyester layer A containing the inert particles A and the above coating layer C has a surface roughness (Ra) of 2.5 to 10.0 nm and a thickness of 8 to 50 nm, handling properties can be improved without impairing the effect of the present invention.
Examples of the inert particles C to be contained in the above coating layer C are the same as those listed for the above inert particles B.
The average particle diameter of primary particles of the inert particles C is 20 to 80 nm, preferably 30 to 70 nm, more preferably 40 to 60 nm. When the average particle diameter is smaller than 20 nm, the slipperiness of the obtained film may become unsatisfactory and when the average particle diameter is larger than 80 nm, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
The surface roughness (Ra) of the coating layer C is 2.5 to 10.0 nm, preferably 3.0 to 9.0 nm, more preferably 3.5 to 8.0 nm. When the surface roughness (Ra) is lower than 2.5 nm, the slipperiness of the obtained film may become unsatisfactory and when the surface roughness is higher than 10.0 nm, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
The thickness of the coating layer C is 8 to 50 nm, preferably 9 to 40 nm, more preferably 10 to 30 nm. When the thickness of the coating layer C is smaller than 8 nm, the inert particles may fall off and when the thickness is larger than 50 nm, the running durability of the obtained tape may become unsatisfactory.
Examples of the binder resin for binding the above inert particles C are the same as those listed for the above inert particles B.
An alkylcellulose or siloxane copolymerized acrylic resin may be added to the coating layer C in order to further improve the strength of the coating film and anti-block properties.
Another polyester layer may be used in place of the above coating layer C to achieve the same purpose.
For instance, when a second polyester layer (may be referred to as xe2x80x9cpolyester layer D (rough layer)xe2x80x9d hereinafter) which contains third inert fine particles (may be referred to as xe2x80x9cinert particles Dxe2x80x9d hereinafter) having an average particle diameter of primary particles of 0.1 to 2.0 xcexcm is formed on the side opposite to the magnetic layer side, when a magnetic tape is to be produced of the polyester layer A (flat layer) containing inert particles A and the above polyester layer D has a surface roughness (Ra) of 2.5 to 10.0 nm and a thickness of preferably 0.1 to 2.0 xcexcm, handling properties can be improved without impairing the effect of the present invention.
Examples of the polyester of the above polyester layer D are the same as those listed for the above polyester layer A. The polyester of the polyester layer D may be different from the polyester of the polyester layer A but preferably the same as the polyester layer A.
Examples of the inert particles D to be contained in the above polyester layer D are the same as those listed for the above inert particles A.
The average particle diameter of the inert particles D is 0.1 to 2.0 xcexcm, preferably 0.2 to 1.5 xcexcm, more preferably 0.3 to 1.0 xcexcm. When the average particle diameter is smaller than 0.1 xcexcm, the slipperiness of the obtained film may become unsatisfactory and when the average particle diameter is larger than 2.0 xcexcm, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
The inert particles D may consist of one type of particles or a mixture of two or more different types of particles. When the inert particles D consist of two or more different types of particles, particles having an average particle diameter of primary particles of 0.1 to 2.0 xcexcm and fine particles having an average particle diameter of primary particles of 0.01 to 0.1 xcexcm such as colloidal silica or alumina having an xcex1, xcex3, xcex4 or xcex8 crystal form may be preferably used. Out of the above examples of the inert particles A, fine particles having an average particle diameter of primary particles of 0.01 to 0.1 xcexcm may also be used.
The content of the fine particles is preferably 0.001 to 5 wt %, more preferably 0.005 to 1 wt %, particularly preferably 0.01 to 0.5 wt %.
The surface roughness (Ra) of the polyester layer D is 2.5 to 10.0 nm, preferably 3.0 to 9.0 nm, more preferably 4.0 to 8.5 nm. When the surface roughness (Ra) is lower than 2.5 nm, the slipperiness of the obtained film may become unsatisfactory and when the surface roughness (Ra) is higher than 10.0 nm, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
The thickness of the polyester layer D is preferably 0.1 to 2.0 xcexcm, more preferably 0.2 to 1.5 xcexcm, much more preferably 0.3 to 1.2 xcexcm. When the thickness is smaller than 0.1 xcexcm, the inert particles may fall off and when the thickness is larger than 2.0 xcexcm. the running durability of the obtained tape may become unsatisfactory.
It is possible and preferred to form the above coating layer C on the surface (side opposite to the magnetic layer side when a magnetic tape is to be produced from the polyester film) of the polyester layer D formed on the above polyester layer A.
The first base film of the present invention may be produced by conventionally known methods and methods accumulated in the industry.
For example, a polyester is molten at a temperature of melting point (Tm) to (Tm+70)xc2x0 C. to form an unstretched film having an intrinsic viscosity of 0.35 to 0.9 dl/g which is then stretched to 2.5 to 5.5 times in a uniaxial direction (longitudinal or transverse direction) at a temperature of (Tgxe2x88x9210) to (Tg+70)xc2x0 C. (Tg: glass transition temperature of the polyester) and then to 2.5 to 5.5 times in a direction perpendicular to the above direction (transverse direction when the film is first stretched in a longitudinal direction) at a temperature of (Tg) to (Tg+70)xc2x0 C. to produce a biaxially oriented film. In this case,the area draw ratio is preferably 9 to 25 times, more preferably 12 to 25 times. Orientation may be either simultaneous biaxial orientation or sequential biaxial orientation.
Further, the above biaxially oriented film may be heat set at a temperature of (Tg+70) to (Tm)xc2x0 C. For example, a polyethylene terephthalate film is preferably heat set at 190 to 230xc2x0 C. The heat setting time is, for example, 1 to 60 sec.
To produce a polyester film, additives other than the above inert particles, such as a stabilizer, colorant and intrinsic viscosity modifier for a molten polymer may be contained in the polyester as required.
The laminate consisting of the polyester layer A and the polyester layer D may be produced by conventionally known methods and methods accumulated in the industry. Out of these, it is preferably produced by coextrusion.
For example, in the case of a biaxially oriented polyester film, a polyester (polyester A) which contains the above inert particles A and will form a flat layer and a polyester (polyester D) which contains the inert particles D and will form a rough layer are laminated together in a molten state in an extrusion nozzle or before the nozzle (the former is called xe2x80x9cmulti-manifold systemxe2x80x9d and the latter is called xe2x80x9cfeed block systemxe2x80x9d) to produce a laminate structure having a suitable thickness ratio which is then coextruded into the form of a film from the nozzle at a temperature of (Tm) to (Tm+70)xc2x0 C. and solidified by quenching to produce an unstretched laminated film.
The formation of the coating layer B and the coating layer C on the polyester layer of the present invention may be carried out by applying aqueous coating solutions.
Coating is carried out on the surface of the polyester layer before it is subjected to the final stretching and the film is preferably stretched in at least a uniaxial direction after coating. The coating film is dried before or during stretching. Coating is preferably carried out on an unstretched laminated film or longitudinally (uniaxially) stretched laminated film, particularly preferably a longitudinally (uniaxially) stretched laminated film. Coating is not particularly limited but roll coating and die coating are used.
The solid content of the above coating solution, particularly an aqueous coating solution is preferably 0.2 to 8 wt %, more preferably 0.3 to 6 wt %, particularly preferably 0.5 to 4 wt %. Other components such as a surfactant, stabilizer, dispersant, ultraviolet light absorber and thickener may be added to the coating solution (preferably an aqueous coating solution) in limits that do not prevent the effect of the present invention.
In the present invention, the Young""s moduli in longitudinal and transverse directions of the laminated film are adjusted to preferably 450 kg/mm2 or more and 600 kg/mm2 or more, more preferably 480 kg/mm2 or more and 680 kg/mm2 or more, much more preferably 550 kg/mm2 or more and 800 kg/mm2 or more, particularly preferably 550 kg/mm2 or more and 1,000 kg/mm2 or more, respectively, to improve the properties such as head touch and running durability of the obtained magnetic recording medium and reduce the thickness of the film.
The crystallinity of the polyester layer is desirably to 50% when the polyester is polyethylene terephthalate and 28 to 38% when the polyester is polyethylene-2,6-naphthalene dicarboxylate. When the crystallinity falls below the lower limit, the heat shrinkage factor tends to become large and when the crystallinity exceeds the upper limit, the abrasion resistance of the film deteriorates whereby white powders are readily generated when the film is brought into sliding contact with the surface of a roll or guide pin.
The first base film of the present invention can be changed into a deposited magnetic recording medium for high-density recording which has excellent electromagnetic conversion characteristics such as output at a short-wavelength range, S/N and C/N, few drop outs and a small error rate by forming a ferromagnetic metal thin film layer made of iron, cobalt, chromium or an alloy or oxide essentially composed thereof on the surface of the polyester layer A (flat layer), preferably the coating layer B by vacuum vapor deposition, sputtering, ion plating or the like, sequentially forming a protective layer of diamond-like carbon (DLC) or the like and a fluorine-containing carboxylic acid-based lubricant layer on the surface of the ferromagnetic metal thin film layer as required according to purpose and use, and further forming a back coat layer on the side opposite to the ferromagnetic layer of the polyester layer A, preferably the surface of the coating layer C or the polyester layer D as required by a known method. This deposited magnetic recording medium is extremely useful as a magnetic tape medium for Hi8 for recording analog signals and digital video cassette recorders (DVC), data 8 mm and DDSIV for recording digital signals.
The first base film of the present invention can be further changed into a metal coated magnetic recording medium for high-density recording which has excellent electromagnetic conversion characteristics such as output at a short-wavelength range, S/N and C/N, few drop outs and a small error rate by applying a coating solution prepared by uniformly dispersing iron or needle-like fine magnetic powders (metal powders) containing iron as the main component into a binder such as polyvinyl chloride or vinyl chloride-vinyl acetate copolymer to the surface of the polyester layer A (flat layer), preferably the coating layer B to form a magnetic layer having a thickness of 1 xcexcm or less, preferably 0.1 to 1 xcexcm, and further forming a back coat layer on the side opposite to the magnetic layer of the polyester layer A, preferably the surface of the coating layer C or the polyester layer D as required by a known method. A non-magnetic layer may be formed on the surface of the polyester layer A, preferably the coating layer B as a layer underlying the metal powder-containing magnetic layer as required by applying a coating solution prepared by dispersing fine titanium oxide particles or the like contained in the non-magnetic layer in the same organic binder as that of the magnetic layer. This metal coated magnetic recording medium is extremely useful as a magnetic tape medium for 8 mm video, Hi8, xcex2-cam SP and W-VHS for recording analog signals and digital video cassette recorders (DVC), data 8 mm, DDSIV, digital xcex2-cam, D2, D3 and SX for recording digital signals.
The first base film of the present invention can be further changed into an oxide coated magnetic recording medium for high-density recording which has excellent electromagnetic conversion characteristics such as output at a short-wavelength range, S/N and C/N, few drop outs and a small error rate by applying a coating solution prepared by uniformly dispersing needle-like fine magnetic powders such as iron oxide or chromium oxide, or lamellar fine magnetic powders such as barium ferrite into a binder such as polyvinyl chloride or vinyl chloride-vinyl acetate copolymer to the surface of the polyester layer A (flat layer), preferably the coating layer B to form a magnetic layer having a thickness of 1 xcexcm or less, preferably 0.1 to 1 xcexcm and further forming a back coat layer on the side opposite to the magnetic layer of the polyester layer A, preferably the surface of the coating layer C or the polyester layer D as required by a known method. A non-magnetic layer may be formed on the surface of the polyester layer A, preferably the coating layer B as a layer underlying the above oxide powder-containing magnetic layer as required by applying a coating solution prepared by dispersing fine titanium oxide particles or the like contained in the non-magnetic layer in the same organic binder as that of the magnetic layer. This oxide coated magnetic recording medium is useful as an oxide coated magnetic recording medium for high-density recording, such as data streamer QIC for recording digital signals.
The above W-VHS is an analog HDTV signal recording VTR and the above DVC can be used to record digital HDTV signals. It can be said that the film of the present invention is a base film very useful for HDTV VTR magnetic recording media.
The magnetic recording medium comprising the first base film of the present invention and a magnetic layer as described above is preferably one of the following magnetic recording media.
(i) A magnetic recording medium comprising a base film which consists of the polyester base film (polyester layer A), the above first coating layer formed on one side of the polyester base film and the above second polyester layer formed on the other side of the polyester base film, and a magnetic layer formed on the first coating layer of the base film.
(ii) Amagnetic recording medium comprising a base film which consists of the polyester base film (polyester layer A), the above first coating layer formed on one side of the polyester base film and the above second coating layer formed on the other side of the polyester. base film, and a magnetic layer formed on the first coating layer of the base film.
A description is subsequently given of the second base film of the present invention.
In the present invention, examples of the thermoplastic resins for forming the first thermoplastic resin layer (called xe2x80x9cthermoplastic resin layer Bxe2x80x9d or xe2x80x9clayer Bxe2x80x9d) and the second thermoplastic resin layer (also called xe2x80x9cthermoplastic resin layer Axe2x80x9d or xe2x80x9clayer Axe2x80x9d) include polyester-based resins, polyamide resins, polyimide resins, polyether-based resins, polycarbonate-based resins, polyvinyl-based resins and polyolefin-based resins. Out of these, polyester-based resins are preferred and aromatic polyesters are particularly preferred.
The thermoplastic resin for forming the first thermoplastic resin layer (may be referred to as xe2x80x9cthermoplastic resin Bxe2x80x9d hereinafter) and the thermoplastic resin for forming the second thermoplastic resin layer (may be referred to as xe2x80x9cthermoplastic resin Axe2x80x9d hereinafter) may be different but preferably the same.
The above aromatic polyesters include polyethylene terephthalate, polyethylene isophthalate, polytetramethylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate and polyethylene-2,6-naphthalate (polyethylene-2,6-naphthalene dicarboxylate). Out of these, polyethylene terephthalate and polyethylene-2,6-naphthalate are preferred.
The polyester may be a homopolyester or copolyester. In the case of a copolyester, examples of a comonomer for polyethylene terephthalate or polyethylene-2,6-naphthalate include other diol components such as diethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, polyethylene glycol, 1,4-cyclohexanedimethanol and p-xylylene glycol, other dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid (in the case of polyethylene-2,6-naphthalate), 2,6-naphthalenedicarboxylic acid (in the case of polyethylene terephthalate) and 5-sodium sulfoisophthalic acid, and oxycarboxylic acid components such as p-oxyethoxybenzoic acid. The amount of the comonomer is 20 mol % or less, preferably 10 mol % or less based on the total of all the diol components in the case of a diol component or the total of all the dicarboxylic acids and oxycarboxylic acids in the case of a dicarboxylic acid component and an oxycarboxylic acid component.
A polyfunctional compound having a functionality of 3 or more such as trimellitic acid or pyromellitic acid may be further copolymerized. In this case, it may be copolymerized in an amount that the polymer is substantially linear, for example, 2 mol % or less.
Examples of a comonomer for polyesters other than polyethylene terephthalate and polyethylene-2,6-naphthalate are the same as above.
The above polyesters are known per se and may be produced by methods known per se.
The thermoplastic resin layer A contains third inert particles (may be referred to as xe2x80x9cinert particles Dxe2x80x9d hereinafter) having an average particle diameter of primary particles of 100 to 2,000 nm in an amount of 0.001 to 5 wt % based on the layer A.
Preferred examples of the inert particles D include inorganic compound fine particles such as (1) heat resistant polymer particles (particles of crosslinked silicone resin, crosslinked polystyrene, crosslinked acrylic resin, melamine-formaldehyde resin, aromatic polyamide resin, polyimide resin, polyamide-imide resin and crosslinked polyesters), (2) metal oxides (such as aluminum sesquioxide, titaniumdioxide, silicondioxide, magnesiumoxide, zincoxide and zirconium oxide), (3) metal carbonates (such as magnesium carbonate and calcium carbonate), (4) metal sulfates (such as calcium sulfate and barium sulfate), (5) carbon (such as carbon black, graphite and diamond), and (6) clay minerals (such as kaolin, clay and bentonite). Out of these, crosslinked silicone resin particles, crosslinked polystyrene resin particles, melamine-formaldehyde resin particles, polyamide-imide resin particles, and fine particles made from aluminum sesquioxide (alumina), titanium dioxide, silicon dioxide, zirconium oxide, synthetic calcium carbonate, barium sulfate, diamond and kaolin are preferred. More preferred are crosslinked silicone resin particles, crosslinked polystyrene resin particles, and fine particles made from aluminum sesquioxide (alumina), titanium dioxide, silicon dioxide and calcium carbonate.
The average particle diameter (dD) of primary particles of the inert particles D is 100 to 2,000 nm, preferably 200 to 1,500 nm, more preferably 200 to 1,000 nm, particularly preferably 200 to 800 nm.
The content of the inert particles D is 0.001 to 5 wt %, preferably 0.01 to 4 wt %, more preferably 0.03 to 3 wt %, particularly preferably 0.05 to 2.0 wt % based on the layer A.
When the average particle diameter of primary particles of the inert particles D is smaller than 100 nm or when the content thereof is lower than 0.001 wt % based on the layer A, winding properties and anti-block properties become unsatisfactory. When the average particle diameter is larger than 2,000 nm or when the content is higher than 5 wt % based on the layer A, the surface of the layer B becomes rough by the shape transfer of protrusions to the surface of the layer B or the protrusions thrusting up the layer B from below, thereby deteriorating electromagnetic conversion characteristics.
The inert particles D may consist of one type of particles or a mixture of two or more different types of particles. When the inert particles D consist of a mixture of two or more different types of particles, colloidal silica and fine particles such as alumina having an xcex1, xcex3, xcex4 or xcex8 crystal form may be preferably used as second and third particles (fine particles) having a smaller average particle diameter of primary particles than the average particle diameter dD of primary particles of the above inert particles D. Out of the above examples of the inert particles D having an average particle diameter dD, fine particles having a small average particle diameter may also be used as the second and third particles (fine particles).
The average particle diameter of the fine particles is preferably 5 to 400 nm, more preferably 10 to 300 nm, particularly preferably 30 to 250 nm and preferably 50 nm or more, more preferably 100 nm or more, particularly preferably 150 nm or more smaller than the above average particle diameter dD. The total content of the second and third particles (fine particles) is preferably 0.005 to 1 wt %, more preferably 0.01 to 0.7 wt %, particularly preferably 0.05 to 0.5 wt % based on the layer A.
The thermoplastic resin layer A contains an ester wax of an aliphatic monocarboxylic acid having 8 or more carbon atoms and a polyhydric alcohol in an amount of 0.001 to 10 wt % based on the layer A.
The number of carbon atoms of the above aliphatic monocarboxylic acid is 8 or more, preferably 8 to 34. When the number of carbon atoms is smaller than 8, the heat resistance of the obtained ester wax becomes unsatisfactory whereby the aliphatic monocarboxylic acid is easily decomposed under the heating condition for dispersing the ester wax in the thermoplastic resin A.
Examples of the aliphatic monocarboxylic acid having 8 or more carbon atoms include pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, melissic acid, hentriacontanoic acid, petroselinic acid, oleic acid, erucic acid, linoleic acid and acid mixtures containing these.
The alcohol component of the ester wax of the present invention is a polyhydric alcohol having 2 or more hydroxyl groups. From the viewpoint of heat resistance, it is preferably a polyhydric alcohol having 3 or more hydroxyl groups. If a monoalcohol is used, the heat resistance of the formed ester wax will become unsatisfactory. Preferred examples of the polyhydric alcohol having 2 hydroxyl groups include ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, diethylene glycol, triethylene glycol and polyethylene glycol. Examples of the polyhydric alcohol having 3 or more hydroxyl groups include glycerin, erythritol, threitol, pentaerythritol, arabitol, xylitol, talitol, sorbitol and mannitol.
The ester wax obtained from the above aliphatic monocarboxylic acid and polyhydric alcohol is a monoester, diester or triester, depending on the number of hydroxyl groups of the polyhydric alcohol. From the viewpoint of heat resistance, a diester is more preferred than a monoester and a triester is more preferred than a diester. Preferred examples of ester wax include sorbitan tristearate, pentaerythritol tribehenate, glycerin tripalmitate and polyoxyethylene distearate.
The above ester wax may be a partly saponified ester wax consisting of an aliphatic monocarboxylic acid and a polyhydric alcohol. The partly saponified ester wax is obtained by partly esterifying a higher fatty acid having 8 or more carbon atoms with a polyhydric alcohol and then saponifying the partly esterified product with a metal hydroxide having a valence of 2 or more. Examples of the partly saponified ester wax include Wax E, Wax OP, Wax O, Wax OM and Wax FL (trade names of Hoechst AG) obtained by saponifying a montanic acid diol ester with calcium hydroxide.
The above ester waxes may be used alone or in combination of two or more.
The thermoplastic resin layer A contains the above ester wax in an amount of 0.001 to 10 wt %, preferably 0.01 to 5 wt %, more preferably 0.05 to 2 wt %, particularly preferably 0.1 to 1 wt % based on the layer A. When the content of the ester wax in the layer A is lower than 0.001 wt %, the effect of improving blocking is not obtained. When the content is higher than 10 wt %, a large amount of a wax component is transferred to the opposite side of the rolled film by bleed-out in the film production process. Therefore, adhesion between a metal deposited layer and the base film is prevented disadvantageously.
The water contact angle of the surface not in contact with the layer B of the above thermoplastic resin layer A is 70 to 90xc2x0, preferably 71 to 89xc2x0, more preferably 72 to 88xc2x0, particularly preferably 74 to 86xc2x0. When the water contact angle is smaller than 70xc2x0, the effect of improving blocking is not obtained. When the water contact angle is larger than 90xc2x0, coating becomes nonuniform in the step of applying a back coat layer.
The first thermoplastic resin layer (may be referred to as xe2x80x9cthermoplastic resin layer Bxe2x80x9d hereinafter) is existent on the magnetic layer side, when a magnetic tape is to be produced, of the polyester film of the present invention in order to improve the handling properties and characteristic properties of the magnetic tape at the time of producing or processing the film.
The surface roughness WRa of the thermoplastic resin layer B is 0.1 to 4 nm, preferably 0.2 to 3.5 nm, more preferably 0.3 to 3.0 nm, particularly preferably 0.4 to 2.5 nm. When WRa is less than 0.1 nm, film production becomes extremely difficult and when WRa is more than 4 nm, electromagnetic conversion characteristics deteriorate.
This surface roughness (WRa) can be adjusted by the particle diameter and/or amount of the inert particles to be contained in the thermoplastic resin layer B.
The thermoplastic resin layer B may not contain particles substantially or may contain inert fine particles (may be referred to as inert particles En hereinafter).
When the thermoplastic resin layer B does not contain particles substantially, a magnetic recording medium having excellent electromagnetic conversion characteristics is obtained advantageously.
When particles are added to the thermoplastic resin layer B in limits that do not exert a bad influence upon electromagnetic conversion characteristics, running durability is improved. Stated more specifically, the inert particles E having a volume shape coefficient of 0.1 to xcfx80/6 and an average particle diameter of primary particles of 30 to 400 nm are preferably contained in the thermoplastic resin layer B in an amount of 0.001 to 0.2 wt %.
Preferred examples of the inert particles E are the same as those listed for the above inert particles A.
The inert particles E have a volume shape coefficient (f) represented by the following equation (I) of 0.1 to xcfx80/6, preferably 0.2 to xcfx80/6, more preferably 0.4 to xcfx80/6:
f=V/R3xe2x80x83xe2x80x83(I)
wherein f is a volume shape coefficient, V is the volume (xcexcm3) of each particle and R is the average particle diameter (xcexcm) of the particles.
The particles having a volume shape coefficient (f) of xcfx80/6 are globular (spherical). That is, the particles having a volume shape coefficient (f) of 0.4 to xcfx80/6 are substantially globular, spherical or oval like a rugby ball which are preferred as the inert particles E. The particles having a volume shape coefficient (f) of less than 0.1, for example, flaky particles deteriorate running durability disadvantageously.
The average particle diameter dE of the inert particles E is 30 to 400 nm, preferably 40 to 200 nm, more preferably 50 to 100 nm. When the average particle diameter dE is smaller than 30 nm, the slipperiness of the obtained film may become unsatisfactory and when the average particle diameter dE is larger than 400 nm, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
The inert particles E may consist of one type of particles or a mixture of two or more different types of particles.
When the inert particles E are contained in the thermoplastic resin layer B, the content of the inert particles E in the thermoplastic resin layer B is 0.001 to 0.2 wt %, preferably 0.01 to 0.1 wt %, more preferably 0.02 to 0.05 wt % based on the layer B. When the content is lower than 0.001 wt %, the slipperiness of the obtained film may become unsatisfactory and when the content is higher than 0.2 wt %, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
When the first coating layer which contains 0.5 to 30 wt % of the second inert fine particles (may be referred to as xe2x80x9cinert particles Bxe2x80x9d hereinafter) having an average particle diameter of 10 to 50 nm and a volume shape coefficient of 0.1 to xcfx80/6 is formed on the surface not in contact with the thermoplastic resin layer A of the thermoplastic layer B, a metal deposited magnetic recording medium having excellent running durability is obtained advantageously.
The resin for forming the first coating layer is preferably an aqueous polyester resin, aqueous acrylic resin or aqueous polyurethane resin, particularly preferably an aqueous polyester resin.
Examples of the aqueous polyester resin are the same as those listed for the first base film of the present invention.
The inert particles B contained in the first coating layer are preferably inert particles which hardly settle in a coating solution and have relatively low specific gravity. Preferred examples of the inert particles B include heat resistant polymer particles such as crosslinked silicone resin, crosslinked acrylic resin, crosslinked polystyrene, melamine-formaldehyde resin, aromatic polyamide resin, polyamide-imide resin, crosslinked polyesters and wholly aromatic polyesters, silicon dioxide (silica) and calcium carbonate. Particularly preferred are crosslinked silicone resin particles, silica particles and core-shell type organic particles (core: crosslinked polystyrene, shell: polymethyl methacrylate).
The average particle diameter dB of primary particles of the inert particles B is 10 to 50 nm, preferably 15 to 45 nm. more preferably 18 to 40 nm. When the average particle diameter dB is smaller than 10 nm, the slipperiness of the obtained film may become unsatisfactory and when the average particle diameter dB is larger than 50 nm, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
The inert particles B have a volume shape coefficient (f) represented by the above equation (I) of 0.1 to xcfx80/6, preferably 0.2 to xcfx80/6, more preferably 0.4 to xcfx80/6. The particles having a volume shape coefficient (f) of less than 0.1, for example, flaky particles make it difficult to obtain satisfactory running durability.
The content of the inert particles B is 0.5 to 30 wt %, preferably 2 to 20 wt %, more preferably 3 to 10 wt % based on the solid content of the first coating layer. When the content is lower than 0.5 wt %, the slipperiness of the obtained film may become unsatisfactory and when the content is higher than 30 wt %, the electromagnetic conversion characteristics of the obtained magnetic recording medium may become unsatisfactory.
The total thickness of the laminated thermoplastic resin film which is the second base film of the present invention is generally 2.5 to 20 xcexcm, preferably 3.0 to 10 xcexcm, more preferably 4.0 to 10 xcexcm. The thickness of the thermoplastic resin layer A is preferably xc2xd or less, more preferably ⅓ or less, particularly preferably xc2xc or less of the total thickness of the laminated thermoplastic resin film. The thickness of the thermoplastic resin layer B is preferably xc2xd or more, more preferably ⅔ or more, particularly preferably xc2xe or more of the total thickness of the laminated thermoplastic resin film. The thickness of the coating layer C is generally 1 to 100 nm, preferably 2 to 50 nm, more preferably 3 to 10 nm, particularly preferably 3 to 8 nm.
The laminated thermoplastic resin film of the present invention may be produced by conventionally known methods and methods accumulated in the industry. Out of these, the laminate structure consisting of the thermoplastic resin layer A and the thermoplastic resin layer B is preferably produced by coextrusion and the first coating layer is preferably formed by coating.
For example, in the case of a biaxially oriented polyester film, the thermoplastic resin A which contains the above inert particles D and ester wax finely dispersed therein and the thermoplastic resin B which contains the inert particles E as required are filtered with high accuracy and laminated together in a molten state in an extrusion nozzle or before the nozzle (the former is called xe2x80x9cmulti-manifold systemxe2x80x9d and the latter is called xe2x80x9cfeed block systemxe2x80x9d) to produce a laminate structure having the above preferred thickness ratio which is then coextruded into the form of a film from the nozzle at a temperature of melting point (Tm) to (Tm+70)xc2x0 C. and solidified by quenching with a cooling roll at 40 to 90xc2x0 C. to produce an unstretched laminated film. Thereafter, the above unstretched laminated film is stretched to 2.5 to 8.0 times, preferably 3.0 to 7.5 times in a uniaxial direction (longitudinal or transverse direction) at a temperature of (Tgxe2x88x9210) to (Tg+70)xc2x0 C. (Tg: glass transition temperature of the polyester) and then to 2.5 to 8.0 times, preferably 3.0 to 7.5 times in a direction perpendicular to the above direction (transverse direction when it is first stretched in a longitudinal direction) at a temperature of (Tg) to (Tg+70)xc2x0 C. in accordance with a commonly used method. The film may be further stretched in a longitudinal direction and/or transverse direction as required. That is, two-stage, three-stage, four-stage or multi-stage orientation may be carried out. The total draw ratio is generally 9 times, preferably 12 to 35 times, more preferably 15 to 30 times.
Further, the above biaxially oriented film is heat set to be crystallized at a temperature of (Tg+70) to (Tmxe2x88x9210)xc2x0 C., for example, 180 to 250xc2x0 C. in the case of a polyethylene terephthalate film to provide excellent dimensional stability. The heat setting time is preferably 1 to 60 sec.
To produce a laminated thermoplastic resin film, additives other than the above inert particles, such as a stabilizer, colorant and intrinsic viscosity modifier for a molten polymer may be contained in the thermoplastic resins A and B as required.
The formation of the first coating layer on the thermoplastic resin layer B of the present invention may be carried out by applying an aqueous coating solution.
Coating is carried out on the surface of the thermoplastic resin layer B before it is subjected to the final stretching, and the film is preferably stretched in at least a uniaxial direction after coating. The coating film is dried before or during stretching. Coating is preferably carried out on an unstretched laminated film or longitudinally (uniaxially) stretched laminated film, particularly preferably longitudinally (uniaxially) stretched laminated film. Coating is not particularly limited but roll coating and die coating are used.
The solid content of the above coating solution, particularly aqueous coating solution is preferably 0.2 to 8 wt %, more preferably 0.3 to 6 wt %, particularly preferably 0.5 to 4 wt %. Other components such as a surfactant, stabilizer, dispersant, ultraviolet light absorber and thickener may be added to the coating solution (preferably aqueous coating solution) in limits that do not prevent the effect of the present invention.
In the present invention, to obtain a thin magnetic recording medium having improved properties such as head touch and running durability, the Young""s moduli in longitudinal and transverse directions of the laminated film are adjusted to generally 450 kg/mm2 or more and 600 kg/mm2 or more, preferably 480 kg/mm2 or more and 680 kg/mm2 or more, more preferably 550 kg/mm or more and 800 kg/mm2 or more, particularly preferably 550 kg/mm2 or more and 1,000 kg/mm2 or more, respectively.
The crystallinity of the thermoplastic resins A and B is desirably 30 to 50% when the thermoplastic resins are polyethylene terephthalate and 28 to 38% when the thermoplastic resins are polyethylene-2,6-naphthalate. Below the lower limit, the thermal shrinkage factor of the film becomes large and above the upper limit, the abrasion resistance of the film degrades and white powders are easily generated upon contact with the surface of a roll or guide pin.
According to the present invention, there are also provided a magnetic recording medium comprising a laminated thermoplastic resin film which comprises the above thermoplastic resin layer A and the above thermoplastic resin layer B formed on one side of the thermoplastic resin layer B as a base film and a magnetic recording medium comprising a laminated thermoplastic resin film which comprises the above thermoplastic resin layers A and B and a first coating layer formed on the side not in contact with the thermoplastic resin layer A of the thermoplastic resin layer B as a base film.
Out of these, preferred is a magnetic recording medium comprising a base film which consists of a laminated thermoplastic resin base film as the second base film of the present invention and the above first coating layer formed on the surface of the first thermoplastic resin layer not in contact with the second thermoplastic resin layer of the base film, and a magnetic layer formed on the first coating layer of the base film.
It should be understood that a description of the first base film is applied to the process for producing a magnetic recording medium from the second base film of the present invention, and the application, magnetic layer used and the like of the magnetic recording medium directly or with modifications obvious to people of ordinary skill in the art.